From now on, no matter you are Windows or Mac users, you can make your own iPhone Ringtone easily, what you need are:
Tipard iPhone Ringtone Maker (http://www.macdvdtoiphone.com/iphone-ringtone-maker.html)(For Windows)
Aiseesoft iPhone Ringtone Maker for Mac (http://www.macdvdtoiphone.com/as-iphone-ringtone-maker-for-mac.html)(For Mac)

The following content will show you the steps:
For Windows users:
Step 1: Download and run Tipard iPhone Ringtone Maker (http://www.macdvdtoiphone.com/download/tp-iphone-ringtone-maker.exe)

Step 2: Click “Browse…” button on the right side of "Input File" to import the file(audio or video file) that you want to make ringtone from it.
Step 3: Click http://www.macdvdtoiphone.com/images/guide/iphone-ringtone-maker/play-n.jpg button to listen the music to find the segment that you want to use it as ringtone.
Then drag and click the start & end slider to set your wanted segment, or type the start & end time in the corresponding text box directly to get the exact segment. Click http://www.macdvdtoiphone.com/images/guide/iphone-ringtone-maker/preplay-n.jpg to pre-listen the converted audio before generate.
Step 4: Click “Browse…” button on the right side of "Local Output Folder" to choose the output destination.
Step 5: Check "Export to iPhone" option, the converted ringtone will be load to your iPhone directly.
Step 6: After all the settings are finished, click “Generate” button to begin making your own iPhone ringtone.

Key featurs
These two iPhone Ringtone Maker can convert almost all mainstream video/audio formats to iPhone ringtone M4R format. Then transfer converted ringtones to iPhone directly without iTunes
Both allow you to clip any music and video segment that you like as iPhone ringtone.
3. Both can play the music before converting with built-in player to ensure it is just the ringtone you want when someone calls you.

http://www.macdvdtoiphone.com/images/guide/iphone-ringtone-maker/interface-mac-n.jpg
Step 2: Click “Browse…” button on the right side of "Input File" to import the file(audio or video file) that you want to make ringtone from it.
Step 3: Click http://www.macdvdtoiphone.com/images/guide/iphone-ringtone-maker/play-mac-n.jpg button to listen the music to find the segment that you want to use it as ringtone.
Then drag and click the start & end slider to set your wanted segment, or type the start & end time in the corresponding text box directly to get the exact segment. Click http://www.macdvdtoiphone.com/images/guide/iphone-ringtone-maker/prelisten-mac-n.jpg to pre-listen the converted audio before generate.
Step 4: Click “Browse…” button on the right side of "Local Output Folder" to choose the output destination.
Step 5: Check "Export to iPhone" option, the converted ringtone will be load to your iPhone directly.
Step 6: After all the settings are finished, click “Generate” button to begin making your own iPhone ringtone.

Here i also want to recommend a powerful tool for iPhone users: which is Tipard iPhone Transfer (http://www.topsevenreviews.com/tipard-iphone-transfer.html)
With this tool, you can transfer video to iPhone/iPhone to PC/iPhone to iPhone
Preparation:Install and run Tipard iPhone Transfer (http://www.topsevenreviews.com/download/tipard/iphone-transfer.exe)

Step 1: connect your iPod/iPhone to your computer via USB cable
Step 2: According your needs to select the the functions
If you want to import video/audio files to your iPhone, clickhttp://www.topsevenreviews.com/guide/tipard-ipod-transfer-pro/files-to-ipod.jpg
If you want to transfer iPhone files to PC, click http://www.topsevenreviews.com/guide/tipard-ipod-transfer-pro/ipod-to-pc.jpg

If you want to transfer iPhone to iPhone,click http://www.topsevenreviews.com/guide/tipard-ipod-transfer-pro/ipod-to-ipod.jpg
Step 3: After you have finished the above two steps,just follow the instructions on it to complete your demands.